schema.org : Java Glossary

schema.org provides a collection of schemas, i.e.,
html tags, that webmasters can use to markup their pages in ways recognized by major
search providers. Search engines including Bing, Google, Yahoo! and Yandex rely on
this markup to improve the display of search results, making it easier for people to
find the right web pages.

Many sites are generated from structured data, which is often stored in databases.
When this data is formatted into HTML (Hypertext Markup Language),
it becomes very difficult to recover the original structured data. Many
applications, especially search engines, can benefit greatly from direct access to
this structured data. On-page markup enables search engines to understand the
information on web pages and provide richer search results in order to make it easier
for users to find relevant information on the web. Markup can also enable new tools
and applications that make use of the structure.

A shared markup vocabulary makes it easier for webmasters to decide on a markup
schema and get the maximum benefit for their efforts. So, in the spirit of
sitemaps.org, search engines have come together to
provide a shared collection of schemas that webmasters can use.

They call the HTML markup tags, microdata. The
HTML5 (Hypertext Markup Language v 5) syntax is typically goofy, not schema.org’s fault. However, their
documentation is extremely clear and easy to follow. This is not rocket science.
Their site uses a series of gradually more complex examples. I hope they eventually
add examples for numbers and bounds. Here is some HTML
with microdata tags added:

If you have look at the page, http://schema.org/Movie, it will tell you what the tag
means and its associated properties.

For example, I have berated online bookstores for not having a standard way to
mark their pages about books to let a screenscraper know in a standard way whether
the book in is or out of stock. Powells now uses the schema.org scheme. Books that are in stock are marked in the body,
not the header:

Unfortunately, they put the InStock tag on all books.
They should use OutOfStock on ones out of stock.
The possible values include:

Discontinued

InStock

InStoreOnly

LimitedAvailability

OnlineOnly

OutOfStock

PreOrder

SoldOut

That does not look like kosher HTML5, but it is. <link can now be used in the body, not just the header.

Originally, you were supposed to include a link like this:<link rel="schema.dcterms" href="http://purl.org/dc/terms/">
Then purl.org started redirecting this to:<link rel="schema.dcterms" href="http://dublincore.org/documents/2012/06/14/dcmi-terms/?v=terms#">
No matter which way you code it, some validators will complain. You could get around the problem by leaving this out altogether.